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Please indicate whether you can or cannot open the windows advanced troubleshooting menu on the computer. If you can there should be options for system restore, startup repair, startup options, command prompt, reset with save files, reset with remove
files, backup image.

1) When you power on the computer what do you see and what do your hear?

2) Is the computer a desktop or notebook?

3) What was the error message and what was the error code?

4) Find a flash drive that you can format ( > or = 8 GB)

5) Create a bootable windows 7 iso:

https://www.microsoft.com/en-us/software-download/windows7

6) Find the keyboard key to boot to the bios boot menu:

http://www.disk-image.com/faq-bootmenu.htm

7) Insert the bootable windows 7 iso into any USB port

8) repetitively click the applicable keyboard key to open the BIOS boot menu

9) If it is a custom computer open the BIOS to temporarily change the BIOS boot order so the the USB drive is on top.

10) Select external USB hard drive

11) It may take 5 - 10 minutes for the iso to load while viewing the Windows icon

12) Select language, time, currency, and keyboard, or click next

13) Click torubleshoot

14) navigate in the the windows advanced troubleshooting menu to system restore

15) select the oldest restore point. Try every restore point moving towards the most recent one. If all restore points fail or if there are no restore points move to the next step.

Since you can't boot into Safe Mode, it is suggested that you can use the repair media to do a startup repair, please refer to:http://www.dell.com/support/article/sg/en/sgdhs1/sln151680/run-startup-repair-on-a-dell-pc-with-a-windows-operating-system?lang=en

Note: this is a 3rd party link, we don't have any warranties on this website. It's just for your convenience

If startup repair can't help to fix the boot problem, it is suggested that you insert the installation media and fix the corrupted system by doing a clean install. Remember to backup the files before you format the drive.

Please remember to mark the replies as answers if they help.
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